1. Field of the Invention
The present invention relates to a high definition television (HDTV) for obtaining an image of higher definition by increasing scanning lines or bandwidth of an image signal. More particularly to a method of 90.degree. phase-shift modulation and demodulation using a phase locked loop (PLL) and a circuit thereof a pilot signal is inserted to the overscan interval of a standard image signal. The phases of the image carrier waves between transmission and receipt are locked so as to be in the same phase. The pilot signal is used as a reference to remove the attenuation of a detected signal due to the phase error generated by a 90.degree. phase-shift modulation during transmission and receipt crosstalk between channels is also significantly reduced.